High molecular weight, water-soluble polymers are important articles of commerce. They are used in a great number of industrial processes to effect the separation of solid matter from aqueous streams by coagulation, flocculation, clarification, settling, retention and other mechanisms. A widely used form of these products is the water-in-oil emulsion which can be metered and pumped with or without a separately packaged inverting agent (usually after dilution in water) into a substrate system. Presently hundreds of millions of pounds of such water-in-oil emulsions are sold and used world-wide, in municipal and industrial waste treatments, in process streams in the mining and paper industries, and for enhanced oil recovery.
It is obviously desirable to provide such polymer products in stable compositions. Such an objective has been long sought after, shortly following the time this type of emulsion product was first introduced. For example, Anderson, et al, U.S. Pat. No. 3,826,771 points out that stability is a key factor in water-in-oil emulsions and defines stability as the ability to maintain the dispersion of the polymer particles throughout the emulsion for an extended period of time. Thus, water-in-oil emulsions of the water-soluble polymer, shipped and stored in drums or holding tanks, are desired with non-settling properties, so that dispensing of the product for its end-use does not require redispersing of the emulsion.
Generally, such a goal is achieved by reducing active polymer solids. However, this approach, while providing more stable products, leads to high shipping costs, larger storage facilities on site with the corresponding inconveniences and economic penalties.
The use of co-surfactants is well known in the literature and in the patent prior art. Becher in "Emulsions Theory and Practice; p 96, Reinhold Publishing Corporation, New York, 1957, discusses the stabilization of interfaces in oil-in-water emulsions using pairs of surfactants. Current art in the water-in-oil emulsions of water-soluble polymers include U.S. Pat. Nos. 4,672,090; 4,764,574; 4,528,321; and 4,024,097. Of these only '090 and '097 teach the use of the fatty alkanolamides in the surfactant pair. However, '090 teaches the use of sorbitan ester adducts as co-surfactants, and it has been found that such esters lead to high sedimentation, induce higher bulk viscosities and reduce stability. Slovinsky ('097) employs the fatty alkanolamides alone or teaches the use of co-surfactants which are ionic emulsifiers and which have very high HLB values. However, emulsifiers with high HLB values do not function well as co-surfactants producing unstable emulsions, frequently even in the preparative stage.
In the early development of water-in-oil emulsions containing water-soluble polymers for the treatment of process and waste streams in the water treating, paper and mining industries, especially those water soluble polymers containing acrylamide monomer units, active solids contents were restricted to 10 to 20% of the overall weight of the emulsion. For example, East German Patent No. 125,854 employs long chain amide and polyether surfactants to produce water-in-oil suspensions, but the active solids taught in the examples of this patent are all below 20%. Moreover, if one runs a polymerization using this teaching with the very low continuous phase (oil) ratio indicated, a coalescence of the dispersed phase occurs and a creamy product results. Creams are, by definition, of high viscosity (&gt;10,000 mPa.s) and non-pourable. If a sedimentation test is run to demonstrate settling under field conditions, a complete sludge is obtained because there is insufficient oil present to keep the polymer particles from sticking to one another.
Current technology does allow water-in-oil emulsions to be prepared at 25% active solids or greater, but this is normally accomplished by increasing the active monomer contents in the aqueous phase and not by decreasing the oil content. Even still, such an advance is achieved at the expense of bulk viscosity of the finished emulsion, and at the expense of stability, usually with high sedimentation occurring on standing.
In fact, it is often deemed necessary to remove water or oil by a separation process in the manufacturing plant and before shipping in order to increase solids. Usually this is done by an evaporative process which is time-consuming and costly. In the present invention, overall active (polymer) solids are maintained above 20%, preferably at levels of 25 to 45%. However, if it is deemed desirable to concentrate the emulsions to a higher solids level this can be accomplished by an evaporative process.